Replace fluid/reservoir asap
That's what mine was doing before the pump failed. Change the fluid soon and you may save the pump. I sucked it out with one of the vacuum pump things. Then refill reservoir, run it some and do it again, repeat a few times. Better yet, replace the reservoir especially on a car this old.
There is a filter in the bottom of the reservoir, its not serviceable, just replace reservoir; about $40.
If you don't catch it soon enough the pump will fail, you'll know that by the difficult steering, though the car can be driven.